Poor metabolic control, hypertension and microangiopathy independently increase the transcapillary escape rate of albumin in diabetes

Abstract

Available evidence indicates that poor metabolic control and raised blood pressure each accelerate the development of diabetic microangiopathy. Microangiopathy is associated with excess albumin deposition in capillary basement membranes and it has been suggested that increased extravasation of plasma constituents may lead to basement membrane thickening. We measured the transcapillary escape rate of albumin, an indicator of the rate of extravasation of intravascular albumin from the circulation per unit time, following intravenous injection of ¹²⁵I-human serum albumin. We examined the independent effects on the transcapillary escape rate of albumin of non-ketotic poor metabolic control, hypertension and microangiopathy. We studied non-diabetic control subjects and diabetic patients, initially when in non-ketotic poor metabolic control and again when control had been improved. We also studied normotensive well-controlled diabetic patients without microangiopathy, normotensive well-controlled diabetic patients with microangiopathy, hypertensive well-controlled diabetic patients without microangiopathy and hypertensive well-controlled diabetic patients with microangiopathy. The transcapillary escape rate of albumin was similar in non-diabetic control subjects (5.5±0.7%/h) and in both Type 1 (5.3±1.2%/h) and Type 2 (5.1±0.6%/h) normotensive diabetic patients without long-term complications. During poor metabolic control the transcapillary escape rate of albumin was significantly higher than in non-diabetic subjects (8.8±0.8%/h and 5.5±0.7%/h respectively, p< 0.01). With improved control values fell significantly to 6.3±0.9%/h (pppp<0.02). We conclude that the transcapillary escape rate of albumin is independently elevated by poor metabolic control, by hypertension and by microangiopathy.